In modern times, electronic communication becomes more and more popular.
US 2005/0021963 A1 discloses a system for and a method of, proving the transmission, receipt and content of a reply to an electronic message. A server receives a message from a sender and transmits the message to a recipient. The server receives from the recipient an attachment as an indication of the opening of the message at the recipient and relating to the message route between the server and the recipient. The server transmits to the sender the message and the attachment and their encrypted digital fingerprints and expunges the transmitted information. To subsequently authenticate the message and the attachment, the sender transmits to the server what the server has previously transmitted to the sender. The server then prepares a digital fingerprint of the message and decrypts the encrypted digital fingerprint of the message and compares these digital fingerprints to authenticate the message. The server performs the same routine with respect to the attachment and the encrypted digital fingerprint of the attachment to authenticate the attachment.